1. Field of the Invention.
The Invention relates generally to an electrode for electric arc furnaces, and particularly to a composite electrode comprising a liquid-cooled long-lived but consumable upper portion attached to a conventional electrode (or consumable tip portion) joined to the upper portion by liquid-cooled connection means.
2. Description of the Prior Art.
The conventional material employed in electrodes for electric arc furnaces is graphite. These electrodes are consumed in use, for example in electric arc steel making furnaces, due to erosion and corrosion caused by oxidation, sublimation, spalling and other factors. This consumption involves tip losses, column breakage losses and particularly surface oxidation losses. An average electric furnace consumes four to eight kilograms of graphite per metric ton of steel produced.
One method for reducing the consumption of graphite electrodes in arc furnaces has been the application of a protective coating or cladding material to the electrodes with oxidation resistant materials. These coatings generally increase the contact resistance to the electrode power clamp, and some are corrosive, as they are based on phosphoric acid. Consequently, they have not found wide acceptance.
Another means for reducing graphite electrode consumption involves the utilization of fully nonconsumable electrode systems. These systems employ full length liquid-cooled electrodes with selected apparatus to protect the electrode from the extreme temperatures of the arc. Although such systems appear in patent literature, this type has not been commercially successful.
It has been suggested heretofore that composite electrodes comprising carbon or graphite portions attached to a water-cooled metallic piece would provide means for reducing electrode consumption in arc furnaces. A number of patents have issued on specific composite electrode designs. For example, U.S. Pat. Nos. 896,429 to Becket; 2,471,531 to McIntyre et al.; 3,392,227 to Ostberg; 4,121,042 and 4,168,392 to Prenn; 4,189,617 and 4,256,918 to Schwabe et al.; and 4,287,381 to Montgomery relate to liquid cooled composite electrodes for arc furnaces. Likewise, European patent application Nos. 50,682; 50,683; and 53,200 by C. Conradty, Nurnburg are directed to composite electrode configurations.